1. Field of the Invention
The present invention relates to a vacuum pump known as a sputter ion pump and, more particularly, relates to a sputter ion pump that has a saddle-shaped electrostatic field and that is free of magnetic field.
2. Discussion of Related Art
A sputter ion pump is a kind of vacuum pump. A conventional sputter ion pump generally includes a cathode and anode electrode, with a high voltage applied therebetween. Electrons spirally move in a high magnetic field and collide with gas molecules. This collision ionizes the gas molecules. The cathode electrode is subjected to a sputtering process by means of the ionized gas molecules activating the surfaces thereof. The ionized gas molecules are absorbed on and/or embedded in the active surfaces of the cathode electrode; and/or are caught by the surfaces of the anode electrode, thereby performing an evacuation of gases. However, the conventional sputter ion pump has a plurality of disadvantages such as a large size, a heavy weight, and a high fabrication cost. Furthermore, a magnetic leakage may occur, and the leakage could affect any peripheral measuring apparatus (e.g., precision and so on).
A new kind of sputter ion pump invented by Tsinghua University utilizes a saddle-shaped electrostatic-field-restricting electron oscillator. This kind of sputter ion pump is free of a magnetic field. For improving the discharge stability in the high vacuum levels and improving the pumping speed, the sputter ion pump adopts a hot cathode to inject electron beams into a discharge zone. This process can improve the vacuum level in a pressure region lower than 2×10−5 Torr. However, the sputter ion pump can only perform the stable discharge process in a narrow region (i.e., in the approximate range from 10−3 to 10−6 Torr). Furthermore, the adoption of the hot cathode electron injection results in the sputter ion pump having a complex structure for the electron emission and having a large power consumption.
What is needed, therefore, is a sputter ion pump with a saddle-shaped electrostatic field that is free of a magnetic field, in which the sputter ion pump has a simplified structure and a low power consumption.